/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.beam.runners.fnexecution.state;

import org.apache.beam.model.fnexecution.v1.BeamFnApi.StateRequest;
import org.apache.beam.model.fnexecution.v1.BeamFnApi.StateResponse;
import org.apache.beam.model.fnexecution.v1.BeamFnStateGrpc;
import org.apache.beam.runners.fnexecution.FnService;
import org.apache.beam.vendor.grpc.v1p26p0.io.grpc.stub.ServerCallStreamObserver;
import org.apache.beam.vendor.grpc.v1p26p0.io.grpc.stub.StreamObserver;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;

import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Throwables.getStackTraceAsString;

/** An implementation of the Beam Fn State service. */
public class GrpcStateService extends BeamFnStateGrpc.BeamFnStateImplBase
        implements StateDelegator, FnService {
    /** Create a new {@link GrpcStateService}. */
    public static GrpcStateService create() {
        return new GrpcStateService();
    }

    private final ConcurrentLinkedQueue<Inbound> clients;
    private final ConcurrentMap<String, StateRequestHandler> requestHandlers;

    private GrpcStateService() {
        this.requestHandlers = new ConcurrentHashMap<>();
        this.clients = new ConcurrentLinkedQueue<>();
    }

    @Override
    public void close() throws Exception {
        Exception thrown = null;
        for (Inbound inbound : clients) {
            try {
                // the call may be cancelled because the sdk harness hung up
                // (we terminate the environment before terminating the service endpoints)
                if (inbound.outboundObserver instanceof ServerCallStreamObserver) {
                    if (((ServerCallStreamObserver) inbound.outboundObserver).isCancelled()) {
                        // skip to avoid call already closed exception
                        continue;
                    }
                }
                inbound.outboundObserver.onCompleted();
            } catch (Exception t) {
                if (thrown == null) {
                    thrown = t;
                } else {
                    thrown.addSuppressed(t);
                }
            }
        }
        if (thrown != null) {
            throw thrown;
        }
    }

    @Override
    public StreamObserver<StateRequest> state(StreamObserver<StateResponse> responseObserver) {
        Inbound rval = new Inbound(responseObserver);
        clients.add(rval);
        return rval;
    }

    @Override
    public StateDelegator.Registration registerForProcessBundleInstructionId(
            String processBundleInstructionId, StateRequestHandler handler) {
        requestHandlers.putIfAbsent(processBundleInstructionId, handler);
        return new Registration(processBundleInstructionId);
    }

    private class Registration implements StateDelegator.Registration {
        private final String processBundleInstructionId;

        private Registration(String processBundleInstructionId) {
            this.processBundleInstructionId = processBundleInstructionId;
        }

        @Override
        public void deregister() {
            requestHandlers.remove(processBundleInstructionId);
        }

        @Override
        public void abort() {
            deregister();
            // TODO: Abort in-flight state requests. Flag this processBundleInstructionId as a fail.
        }
    }

    /**
     * An inbound {@link StreamObserver} which delegates requests to registered handlers.
     *
     * <p>Is only threadsafe if the outbound observer is threadsafe.
     *
     * <p>TODO: Handle when the client indicates completion or an error on the inbound stream and
     * there are pending requests.
     */
    private class Inbound implements StreamObserver<StateRequest> {
        private final StreamObserver<StateResponse> outboundObserver;

        Inbound(StreamObserver<StateResponse> outboundObserver) {
            this.outboundObserver = outboundObserver;
        }

        @Override
        public void onNext(StateRequest request) {
            StateRequestHandler handler =
                    requestHandlers.getOrDefault(request.getInstructionId(), this::handlerNotFound);
            try {
                CompletionStage<StateResponse.Builder> result = handler.handle(request);
                result.whenComplete(
                        (StateResponse.Builder responseBuilder, Throwable t) ->
                                // note that this is threadsafe if and only if outboundObserver is
                                // threadsafe.
                                outboundObserver.onNext(
                                        t == null
                                                ? responseBuilder.setId(request.getId()).build()
                                                : createErrorResponse(request.getId(), t)));
            } catch (Exception e) {
                outboundObserver.onNext(createErrorResponse(request.getId(), e));
            }
        }

        @Override
        public void onError(Throwable t) {
            if (!t.getMessage().contains("cancelled before receiving half close")) {
                // ignore the exception "cancelled before receiving half close" as we don't care
                // about it.
                outboundObserver.onError(t);
            }
        }

        @Override
        public void onCompleted() {
            outboundObserver.onCompleted();
        }

        private CompletionStage<StateResponse.Builder> handlerNotFound(StateRequest request) {
            CompletableFuture<StateResponse.Builder> result = new CompletableFuture<>();
            result.complete(
                    StateResponse.newBuilder()
                            .setError(
                                    String.format(
                                            "Unknown process bundle instruction id '%s'",
                                            request.getInstructionId())));
            return result;
        }

        private StateResponse createErrorResponse(String id, Throwable t) {
            return StateResponse.newBuilder().setId(id).setError(getStackTraceAsString(t)).build();
        }
    }
}
